Phenotypic characterization of ‘non‐T, non‐B’ acute lymphoblastic leukemia by a new panel (BL) of monoclonal antibodies

Peripheral blood and/or bone marrow leukemic cell suspensions from 49 patients with ‘non‐T, non‐B’ acute lymphoblastic leukemia (ALL) were analysed by flow cytometry using a new panel of four monoclonal antibodies. Anti‐BL1 and anti‐BL2 originating from NALM‐6 and B35M lymphoblastoid cell lines, respectively. These antibodies recognize B‐cell differentiation antigens: a heat stable non‐immunoprecipitable antigenic determinant, and a 68 000 daltons glycoprotein molecule, respectively. BL5 and BL6 were derived by immunization with the promyelocytic cell line HL‐60, recognizing antigens present on early hemato‐poietic cells: an 85 000 daltons MW glycoprotein (Pro‐Im1) and a heat stable antigen (Pro‐Im2), respectively. All ALL patients studied had L1 or L2 morphology by the FAB classification and a blast count exceeding 50 per cent. There were 25 males and 24 females. Median age was 8 years (range 1–67 years). Thirty‐nine cases were studied at initial presentation and 10 at relapse. Cells from 46/49 cases expressed BL2 and/or BL1, but were not reactive with BL5 or BL6. Three of 49 cases did not express BL1 or BL2. However, a small percentage of blasts from one case was positive for BL5 (13 per cent) and the other 2 cases were reactive with BL6 (20 per cent and 36 per cent, respectively). These were one adult and 2 pediatric patients that had other ALL markers and achieved a complete remission with appropriate ALL therapy. One of the BL6+ cases relapsed after 19 months with a change in phenotype to BL1+ BL2+ BL5‐ BL6‐. This analysis shows that the majority of ‘non‐T, non‐B’ ALL's do express B‐cell associated antigens (BL1/BL2) argumentative of their B‐cell origin. A small subgroup does not express such antigens and may arise from a more immature cell, since they expressed antigens on early hematopoietic stem cells.